1. Field of the Invention
This invention relates to a document reading device and especially relates to for example a document reading device connected to a personal computer or a work station.
2. Description of the Related Art
As a technological development in information processing engineering, a system for transmitting image information read by an image reading device to a host computer, such as a personal computer, a work station or the like to process the image is currently used.
In the reading operation of such an image reading device, the amount of information read by said image reading device is large compared with the capacity of memory provided in the host computer, therefore the reading operation of the reading means in the reading device is sometimes stopped while scanning manuscript.
Once the operation of the reading means is stopped, the processing of the image information in the host computer will be advanced to restart the reading operation thereof when the transmission of the information becomes possible, and the reading operation can be continued thereafter.
However, when the reading operation is stopped, on restarting the reading operation, it is difficult to restart the reading operation at the exact position at which the reading operation was stopped, due to the transient characteristics of the driving system.
To overcome this problem, the same assignee as that of this invention had already proposed a vertical scanning method in the specification of the Japanese Unexamined Patent Publication No. 61-131673.
In this method, before restarting the reading operation, the driving system for the reading means is set back at a predetermined distance taking the transient characteristics of the driving system into the account, and the reading operation is started again from that position.
However, in the conventional method as explained above, there are many cases in which the position from which the reading operation is restarted after the driving system for the reading means is set back, taking the transient characteristics of the driving system into the account, does not necessarily coincide with the position at which the reading operation was interrupted.
If such a situation occurs, a discontinuous portion of the final image information will be generated at the position at which the reading operation was interrupted, thereby causing the image information thus reproduced to be incorrect.